Original Character Mary Sue Test
Mary sues are big problems in literature because they are often overpowered. These kinds of characters can make a story dull or boring. So that is why you should try to avoid them.
When writing, it's important to take setting and such into context. For example, immortality, beauty, super strong, etc. is fitting for your world and is relativily common, the answer to if they are or arent a mary sue is more ciomplicated.